NAPA and colitis: Elevated recovery of the respiration-proficient E. coli wild type over the respiration-deficient cydA napA narG narZ mutant was consistent with previous reports indicating that DSS-induced colitis increases the luminal bioavailability of oxygen and nitrate (25, 27, 28), but this increase in the competitive index was blunted in DSS-treated mice receiving 5-ASA supplementation (Fig. 1D).